Active pixel sensors are well known in the art. A basic active pixel sensor is described in U.S. Pat. No. 5,471,515. An active pixel sensor typically includes a plurality of pixel circuitry units. Each unit, or xe2x80x9cpixelxe2x80x9d includes a photoreceptor, a buffer, and a select transistor. Some means of resetting the pixel is also provided.
It is desirable to make each pixel as small as possible to enable more pixels to fit on a single chip. For example, a desirable size in current technology is 5xc3x975 xcexcm2. It is also desirable to keep the supply voltages low as possible. For example, it would be useful if an active pixel sensor could operate from a single 1.5 volt battery. This provides limitations on the way in which such a device can operate.
The present application features a new pixel structure which has certain advantages, and can operate using relatively low power.
The present application defines an active pixel unit, that has a charge accumulating part, having a capability of accumulating charge therein; a photoreceptor, connected to said charge accumulating part, and changing an amount of charge therein based on an applied received charge; a reset transistor, having its drain and gate connected together, and connected to reset said charge accumulating part; and a select transistor, also having its drain and gate connected together, and connected to select an output of said charge accumulating part.